System for displaying a point on a transparent or translucent screen

ABSTRACT

The invention provides a system for displaying a luminous point on a screen, the display being visible on both sides of the screen and it being possible to approach either side of the screen without disturbing the display. To this end, use is made of a slightly diffusing or fluorescent screen through which travel three light rays intersecting at the point or dot to be displayed.

United States Patent [191 Chaverebiere de Sal et a1.

[451 Oct. 1, 1974 SYSTEM FOR DISPLAYING A POINT ON A TRANSPARENT OR TRANSLUCENT SCREEN [75] Inventors: Alain Marie Alfred Jean Chaverebiere de Sal, Paris; Alain Jean Thouvenin, Meudon, both of France [73] Assignee: Societe ECA, (Hauts-de-Seine),

France [22] Filed: Mar. 30, 1973 [21] Appl. No.: 346,567

[30] Foreign Application Priority Data Mar 31, 1972 France 72.11578 [52] US. Cl. 353/122, 356/103 [51] Int. Cl. G03b 21/00 [58] Field of Search 353/122; 350/10; 356/103; 240/1 EL [56] References Cited UNITED STATES PATENTS 1,302,353 4/1919 Fredrich 350/10 2,584,777 2/1952 Adolfson 240/1 EL 2,898,880 8/1959 Newton, Jr. 240/1 EL Primary Examiner-Louis R. Prince Assistant Examiner-Steven L. Stephan Attorney, Agent, or Firm-Murray Schaffer [5 7 ABSTRACT The invention provides a system for displaying a luminous point on a screen, the display being visible on both sides of the screen and it being possible to approach either side of the screen without disturbing the display. To this end, use is made of a slightly diffusing or fluorescent screen through which travel three light rays intersecting at the point or dot to be displayed.

11 Claims, 3 Drawing Figures TENTEB T 1974 3.838.917

SYSTEM FOR DISPLAYING A POINT ON A TRANSPARENT OR TRANSLUCENT SCREEN The technical province of this invention is that of luminous displays on screens.

The problem of displaying points of known coordinates on a screen has heretofore received numerous optical, electrical or electronic solutions.

It is already known, for example, to display points on a screen by projections of light thereon or by activating the fluorescent property of points on the screen of a cathoderay tube. However, such methods cannot be used when it is necessary to provide a display which can be viewed from both sides of the screen and which will permit access to either side of the screen without disturbing the display.

The present invention has for its object to allow displaying a luminous point at a variable location on a screen in such manner that it be visible on both sides of the screen, that access be possible to at least one side of the screen in order for example to position at the location of the luminous point, without disturbing the dis play, a convenient material marker so as to leave a trace of said location after the luminous point has shifted or disappeared, and that said material marker be visible on both sides of the screen.

A display system according to this invention accordingly consists of a rectangular screen made of a transparent material which nevertheless possesses a certain capacity for diffusion or fluorescence and through the edge of which are caused to enter, parallel to the plane of the screen, by means of suitable optical means, a plurality three for example of light rays which meet at the point to be displayed. The intersection of these rays produces a bright dot which is visible on both sides of the screen by a process of diffusion or fluorescence.

The descrition which follows with reference to the accompanying non-limitative exemplary drawings will give a clear understanding of how the invention can be carried into practice. I

In the drawings:

FIG. 1 is a plan view of a first possible embodiment of a display system according to this invention;

FIG. 2 is a detail view of one of the corners of the screen,

and

FIG. 3 is a plan view of an alternative embodiment of a display system according to the invention.

Recourse is bad to a flat, thin rectangular screen made of a partly transparent substance possessing to some extent the property of diffusing light. Such substance may be a transparent acrylic resin for example, containing a charge of fine particles in a suitable proportion. Alternatively, recourse may be had to a screen made of a transparent material containing a fluorescent substance capable of being excited by at least one light source to be described hereinafter.

In one form of embodiment of the invention, there is associated to screen 1 a single light source 2 and three optical devices 3, 4 and 5 each positioned in immediate proximity to one of three corners of the screen 1 The light source 2, which is preferably a source of cohcrent light, emits a narrow beam of parallel rays 6 in the direction of the first optical device 3. The latter consists of a partly reflecting mirror 7 having a coefflcient of reflection of 30 percent, and a totallyreflecting mirror 8. Mirrors 7 and 8 are plane mirrors positioned perpendicular to the plane of the screen. Mirror 7 can be swivelled about a pivot 9 lying in its plane and perpendicular to the plane of the screen. Mirror 7 may be positioned anywhere between the limit positions 7 and 7". Mirror 8 has a fixed but adjustable position.

The beam of incident light 6 first strikes the mirror 7 which reflects part of it in the form of a beam a which enters the body of screen I through the edge thereof and which is caused to pass through the point A to be displayed by an appropriate orientation of said mirror. The non-reflected part II of beam 6 passes through mirror 7 and impinges upon mirror 8, the position of which is such that the resultant beam 12 reflected by it travels along the edge I3 of screen 1 towards the second optical device 4.

This second optical device is composed of components similar to those of optical device 3, to wit a partly reflecting mirror I4 (having in this case a reflection coefficient of percent) which can be swivelled about its pivot 15 perpendicular to the plane of the screen. and a totally reflecting mirror 16. In the same manner. there issue from this second optical device 4 a beam h which enters the thickness of the screen and passes through the point A, and a beam 18 reflected along the edge 19 of the screen towards the: third optical device 5.

In contrast to the first two optical devices 3 and .4, optical device consists of a single totally reflecting mirror 20 which can swivel about its pivot 21 perpendicular to the plane of the screen and which reflects the incident beam 18 to form a beam 0 passing through the point A.

Each screen corner having an optical device associated thereto is formed with an arcuate indent 26 cens tered upon the pivot axis of the associated swivelling mirror, which indent allows the beam reflected by said mirror to enter the thickness of the screen without deflection. Further, the coefficients of reflection of the mirrors 7 and 14, such as indicated hereinabove, are chosen so that the luminous intensities of the three beams a, b and c be substantially equal.

The theory of operation of a display system as hereinbefore described is as follows the light source 2 emits a beam 6 which travels along the sides of the screen and in so doing successively meets optical devices 3, 4 and 5 which causes three beams a, b and c to enter the screen through an edge thereof, in a direction parallel to the plane of the screen. By utilizing means (not described herein) which may include a computer and servo controls, the angular position of each of movable mirror 7, l4 and 20 can be so controlled as to cause the beams a, b and c to meet at a single point A having the desired location on the screen which location may be defined by any convenient system of coordinates such as Cartesian or polar coordinates.

The coalescence at the point A of the light diffused or emitted by fluorescence within the screen, by the three beams, causes the target point to be highlighted in relation to the traces due to the beams themselves, and the luminous point is furthermore visible from both sides of the screen. All the above-described phenomena occur in the plane of the screen, as it were, and both sides thereof can be approached without disturbing the display.

The dimensions and angles of deflection of swivelling mirrors 7, l4 and .20 and the dimensions of indents 26 are so chosen that the beam travelling along the edges of the screen is never inadvertently intercepted by these mirrors and so that the point A which is the point of intersection of the three beams a, b and can lie in any desired position on the screen.

The edges of the screen are preferably treated to make them absorb light (with the exception, of course. of the indents), in order to avoid multiple reflections within the screen and thereby produce ghost points. Such treatment can be necessary in particular in cases where the beams a, b and c are liable to strike the edges of the screen at angles in excess of the total-reflection angle, although this can usually be avoided by a judicious choice of the screen dimensions.

An alternative form of embodiment of the invention is illustrated in FIG. 3. The single light source and the optical devices with their mirrors are replaced by three light sources 23, 24, 25 which are preferably lasers. These light sources are positioned at three of the corners of screen 1. The properties of screen 1 remain unchanged, and the beam of light emitted by each of the sources passes through a controlled device 27 where it undergoes variable angular deflection such that the three resultant beams a, b and 0 meet at the desired point A. Preferably, each device 27 is a controlleddeflection electro-optical cell. The same result is obtained in this case as with the first form of embodiment described herein.

In both these exemplary embodiments, the configuration of the display system is such that three light beams define the point to be displayed. Manifestly, two light beams would be sufficient in theory to achieve the re quired object, and elimination of the third beam would have the advantage of reducing the complexity of the system hereinbefore described and of lowering its cost, notably in the second form of embodiment. However, the use of three beams provides better definition and contrast for the point to be displayed, and this over a wider expanse of the screen. Further, the resulting redundancy provides a means of detecting faulty operation of the system since three luminous dots instead of only one would appear if the three light beams did not meet at the same point.

The quality of the punctual display can be improved by defining the point by means of three light beams of different colours. By additively combining these colours, the point to be displayed will be colourcontrasted in relation to the incident beams. Thus if beams of blue. red and green light are used. a white punctual display can be obtained. This particularity, which falls within the scope of the invention, can be obtained in the case of the first embodiment herein described by adopting a source of white light for light source 2 and by interposing a suitable colour filter at the origin of each of light beams a, b and c. The same method would be applicable to the alternative form of embodiment described hereinabove, by using white light emitting sources 23, 24 and 25. Alternatively, these three sources could be formed by three lasers of appropriate colour.

One of the faces of the screen could have a grating of lines overlaid thereon in order to permit ready location of the displayed point by observers.

It goes without saying that changes and substitutions of parts may be made to the embodiments hereinbefore described without departing from the scope of the invention.

What is claimed is:

1. A system for displaying a point on a screen. comprising in combination. one thin flat polygonal screen made of a material capable of transmitting light and possessing the property of revealing to the exterior the presence of a light beam travelling through its bulk, and at two corners of said screen. optical means for causing a narrow beam of parallel light rays to enter the body of the screen in a direction parallel to the plane of said screen in such manner that the several beams meet at a single point to be displayed.

2. A display system according to claim 1, wherein said optical means including a light source directing a narrow beam of parallel light rays towards a first corner of said screen, and positioned. at as many consecutive corners of said screen as it is required to cause light beams to enter said screen and meet at the point to be displayed, an optical system which causes the incident beam to split into two light beams, one of which travels in the direction of the next corner and the other enters the body of said screen in the direction of the point to be displayed, save in the case of the last corner of the screen where the incident beam is not split but is directed in its entirety. by associated optical means towards the point to be displayed.

3. A system according to claim 2, wherein the optical means positioned at the screen corners each consist of a totally reflecting plane mirror perpendicular to the plane of the screen and having a fixed but adjustable position, and of a partly reflecting plane mirror rotatable about a pivot lying in its plane and perpendicular to plane of said screen with the exception of that optical means which is positioned at the last corner and which consists of a single totally reflecting plane mirror rotatable about an axis lying in its plane and perpendicular to the plane of the screen.

4. A display system according to claim 3, wherein at each screen corner into which a light beam penetrates. the screen is formed with an arcuate indent centered upon the axis of rotation of the beam whereby to permit undeflected entry thereof into the body of the screen.

5. A display system according to claim 2, wherein said screen is rectangular and is associated with three light beams which meet at the point to be displayed.

6. A display system according to claim 2, wherein said optical means positioned at screen corners each emit a beam of light of different colour and the several beams merge at their point of intersection to form still another colour.

7. A display system according to claim 1, in which said optical means positioned at at least two of the screen corners are in each case a light source so devised as to cause entry into the body of the screen of a narrow beam of parallel light rays that can be deflected by rotation about an axis perpendicular to the plane of the screen.

8. A display system according to claim 7, wherein an gular deflection of the beam is obtained by electrooptical means.

9. A display system according to claim 1, wherein said optical means are lasers.

10. A display system according to claim 1, wherein said screen is made of a material which possesses a property of fluorescence that can be activated by at least one light source.

H. A display system according to claim I, wherein said screen is made of a substance possessing the property of diffusing light. 

1. A system for displaying a point on a screen, comprising in combination, one thin flat polygonal screen made of a material capable of transmitting light and possessing the property of revealing to the exterior the presence of a light beam travelling through its bulk, and at two corners of said screen, optical means for causing a narrow beam of parallel light rays to enter the body of the screen in a direction parallel to the plane of said screen in such manner that the several beams meet at a single point to be displayed.
 2. A display system according to claim 1, wherein said optical means including a light source directing a narrow beam of parallel light rays towards a first corner of said screen, and positioned, at as many consecutive corners of said sCreen as it is required to cause light beams to enter said screen and meet at the point to be displayed, an optical system which causes the incident beam to split into two light beams, one of which travels in the direction of the next corner and the other enters the body of said screen in the direction of the point to be displayed, save in the case of the last corner of the screen where the incident beam is not split but is directed in its entirety, by associated optical means towards the point to be displayed.
 3. A system according to claim 2, wherein the optical means positioned at the screen corners each consist of a totally reflecting plane mirror perpendicular to the plane of the screen and having a fixed but adjustable position, and of a partly reflecting plane mirror rotatable about a pivot lying in its plane and perpendicular to plane of said screen with the exception of that optical means which is positioned at the last corner and which consists of a single totally reflecting plane mirror rotatable about an axis lying in its plane and perpendicular to the plane of the screen.
 4. A display system according to claim 3, wherein at each screen corner into which a light beam penetrates, the screen is formed with an arcuate indent centered upon the axis of rotation of the beam whereby to permit undeflected entry thereof into the body of the screen.
 5. A display system according to claim 2, wherein said screen is rectangular and is associated with three light beams which meet at the point to be displayed.
 6. A display system according to claim 2, wherein said optical means positioned at screen corners each emit a beam of light of different colour and the several beams merge at their point of intersection to form still another colour.
 7. A display system according to claim 1, in which said optical means positioned at at least two of the screen corners are in each case a light source so devised as to cause entry into the body of the screen of a narrow beam of parallel light rays that can be deflected by rotation about an axis perpendicular to the plane of the screen.
 8. A display system according to claim 7, wherein angular deflection of the beam is obtained by electro-optical means.
 9. A display system according to claim 1, wherein said optical means are lasers.
 10. A display system according to claim 1, wherein said screen is made of a material which possesses a property of fluorescence that can be activated by at least one light source.
 11. A display system according to claim 1, wherein said screen is made of a substance possessing the property of diffusing light. 